Method and apparatus for memory and display

ABSTRACT

A plasma-discharge display and data storage device wherein a glow discharge condition in a gas-filled, dielectric envelope is transferred from a region between a pair of transferor electrode conductors to a region between a pair of transferee electrode conductors by causing an AC voltage applied between the transferee electrode conductors to cause an associated potential field inside the gas-filled envelope to reach a glow-dischargesustaining magnitude prior to the time that the AC voltage applied between the pair of transferor electrode conductors causes an associated potential field within the gas-filled envelope to reach a magnitude sufficient to sustain a glow discharge; and a tapered electrode conductor in which a plasma or glow discharge in the gas occurs preferentially near the wide end of the tapered electrode conductor.

United States Patent McClelland NIETHOD AND APPARATUS FOR MEMORY AND DISPLAY Walter B. McClelland, Park Ridge, 111.

[73] Assignee: Teletype Corporation, Skokie, Ill.

[22] Filed: June 24, 1970 [21] Appl. No.: 49,436

[72] lnventor:

[451 Nov. 28, 1972 Primary Examiner-Roy Lake Assistant Examiner-Lawrence J. Dahl Attorney.l. L. Landis and R. P. Miller [57] ABSTRACT A plasma-discharge display and data storage device wherein a glow discharge condition in a gas-filled, dielectric envelope is transferred from a region between a pair of transferor electrode conductors to a region between a pair of transferee electrode conductors by causing an AC voltage applied between the transferee electrode conductors to cause an associated potential field inside the gas-filled envelope to reach a glow-discharge-sustaining magnitude prior to the time that the AC voltage applied between the pair of transferor electrode conductors causes an associated potential field within the gas-filled envelope to reach a magnitude sufficient to sustain a glow discharge; and a tapered electrode conductor in which -a plasma or glow discharge in the gas occurs preferentially near the wide end of the tapered electrode conductor.

31 Clains, 13 Drawing Figures 1 1 I I I 1 I, qr-22 PATENTEDImv 28 m2 SHEET 2 UF 4 VOLTAGE GENERATOR VOLTAGE GENERATOR PHOTOCELL r FIG.

. 1 I METHOD AND APPARATUS FOR MEMORY DISPLAY FIELD OF THE INVENTION This invention relates to display and memory and more particularly to a method and apparatus for memory and display wherein a gas discharge occurs in an envelope having an inside environment significantly larger than that needed for a single discharge.

. BACKGROUND or THE INVENTION SUNIMARY OF THE INVENTION This invention relates to a plasma discharge device of the type having a gas in a confined area or envelope between a pair of dielectric sheets or coversheets forming an envelope, each sheet having at least one conductor thereon with the conductors being located on the outsides of the sheets and opposite one another across the gas-filled space. The ionization of the gas takes place when a predetermined voltage exists across the gasfilled space inthe envelope formed by the dielectric sheets, causing a portion of the gas to glow momentarily. 1 1

The gas-filled space has an area thatv is significantly greater than the size required to support'a single glow discharge. The shape of the gas-filled envelope relative to the :shape of atleast one of the conductors is such j that, upon the application of a sufficient voltage across the gas in the region of the conductors, the gas thus ionized covers-an area on the dielectric sheet adjacent to at least one of the conductors, which area varies in a j predetermined manner so that the application of voltfield extending from one conductor through one sheet of dielectric glass, the gas, and the other sheet of glass to the other, crossing conductor, causes the gas in the hole in the center glass sheet between the two orthogonal conductors to ionize to a glowing plasma and thus generate a display.

It is known to be possible to operate the display with only the two outer sheets of glass and with the sealed space between the two sheets simply filled with gas with no center sheet. 'One such device is shown on Pages 133-136 of the Mar. 3 l, 1969, issue of Electronics.

Due to thecapacitive nature of the glass sheet and the 't'endancy of the ionized gas to deposit opposite charges on the inside surfaces of the" two outer sheets of glass, such as plasma glow discharge occurs only momentarily in each half-cycle of the input AC electrical signal that is applied between, the two orthogonal conductors. The next half cycle of the input AC voltage signal causes discharge to ,occur at a signal voltage which is less than the voltage would have to be, were it not for the above-mentioned charges on the inside surfaces of the outer two glass sheets. Discharge occurs when the instantaneous signal voltage plus the efiective charge voltage on the dielectric glass sheets equals the breakdown voltage of the gas, taking into account the voltage drop across the capacitors formed by the two outer sheets of dielectric glass. This charge ages of different magnitudes causes the discharges to ,takeplace at different portions of [the dielectric sheet adjacent to different conductors or different portions of the conductors.

In an alternative version of the present invention, a memory or display condition is made to move from one pair of electrode conductors to another pair of electrode conductors. This is accomplished by causing an AC sustaining voltageto occur sooner between the other pair of electrode conductors'than between the one pair of electrode conductors.

' BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of the present invention may be had by referring to the following phenomenon results in the inherent memory of the system since each hole or cell of the system will remember, for a period of time, its previous condition,

that is, whether it tired or not and in which direction or. electricalpolarity it last fired.

Still another object of the present invention is a plasma shift register;

It is a further object of the present invention to advance a glow discharge from one electrode to another in a memory display.

detailed description when considered in conjunction with the accompanying drawings, wherein like reference numbers refer to similar or comparable parts in the several views and wherein:

FIG. 1 shows one tapered conductor on a gas-filled dielectric envelope; v

FIG. 2 is a cross-sectional viewof the device'shown in FIG. 1 taken along line 2-2 of FIG. 1 and showing two glass sheets which together with end pieces form a gas-filled envelope, having conductors positioned on the sides of the glass sheets opposite the gas-filled space;

FIG. 3 shows the gas-filled envelope of FIG. 1 but with the conductor arranged in discrete increments of areas;

FIG. 4 shows an envelope with conductors of uniform width but the envelope is tapered;

FIG. 5 shows .a conductor with discrete areas of uniform width and with a'tapered envelope;

FIG. 6 shows several individual conductors on a single envelope;

FIG. 7 is a cross-sectional view of the envelope of FIG. 6 taken along the line 7--7; FIG. 8 shows an ignition electrode and several tapered electrodes for advancing a glow discharge condition in steps from one electrode to another;

FIG. 9 shows an arrangement of conductors for performing a shift register function according to the present invention;

FIG. 15 shows a two-part orthogonal pattern of conductors .for stepping a signal in either direction, thus forming a bi-directional data shift register;

FIG. 11 shows the shift register of FIG. arranged in a folded configurationthat is particularly useful for display purposes;

FIG. 12 shows the shift register of FIG. 10 with an encoding system and provision for transferring a glow discharge condition from one shift register to another;

and

FIG. 13 illustrates an adaptation of the shift registers of FIGS. 1 l and 12 to encode a font of display characters, advance them to a display panel, and propagate the characters along the display panel. I

DETAILED DESCRIPTION uniform cross-sectional area along its length. Two conductors 28 and 30 are bonded to the outside surfaces of the sheets 20 and 22. The width of the conductor 30 is centers of the discreteareas. Thus, the location of each glow discharge is entirely predictable. g It has been found that, if both of the electrode con- 1 ductors 28 and 30 are of uniform width but if the gastapered along its length, and the other conductor 28 Y has a uniform width over its entire length. The gas is principally a mixture of inert gasses. The preferred mixture comprises approximately 2.5 percent nitrogen and the remainder neon. The envelope 26 can actually be formed by bonding the conductors 28 and to two, thick, rigid, insulating substrates 27 and 29. The coversheets 20 and 22 can then be bonded over the substrates and the conductors.

As the voltage applied between the tapered conductor 30 and the other conductor 28 is raised, the dielectric nature of the glass sheets 20 and 22 and of the gas in the space 26 causes an AC voltage divider effect to occur; and a voltage difference develops between the inside surfaces of the glass sheets 20 and 22. When this voltage difference equals the firing voltage of the gas, the gas ionizes to a plasma and a glow discharge takes place.

The maximum electric field between the two conductors at any location along the length of either of the two conductors 28and 30 occurs atthe center of its width. Due to edge effects, the maximum field due to the applied voltage occurs at the center of the widest portion of the tapered conductor because of the fringing effects of the field at the edges of a parallel plate capacitor such as that formed by the glass and gas between the two conductors. Therefore, glow discharge begins between the conductors 28 and 30 at the center of the widest end of the tapered conductor 30; and as the voltage continues to increase above the minimum voltage necessary to initiate discharge, the

filled space 26 is tapered, as shown in FIG. 4, the ionization and glow discharge will first take place at the widest point in the gas-filled space 26.

Similarly, if the electrode conductor 30 comprises discrete areas of uniform length and width but is positioned over a tapered gas-filled space 26 (FIG. 5), the glow discharge first takes place adjacent the conductor area nearest the wide portion of the gas-filled space 26. This is similar to the phenomenon that occurs with a gas-filled space of uniform width but with a conductor having discrete areas of different size as is shown in FIG. 3.

- INFORMATION TRANSFER It has been found that when a glow discharge occurs,

'charge' collects on the inside surface of the glass coversheet over an area that is wider than the area of the widest portion of the electrode conductor. That is, the charge collects substantially beyond the edge of the electrode conductor. If a send electrode conductor is placed on the same sheet of glass and very near the first electrode conductor, some of the collected charge will also be very near to and may actually overlap the second electrode conductor.

It will be recalled that this charge collected on the inside surface of the glass sheet is the essence of the memory of such a system. This capacitively-collected charge functions to reduce the AC voltage level that must be applied between the opposing electrode conductors in each half-cycle after thein'itial ionization in order to reionize the gas.

If a subsequent voltage were applied to the second electrode conductor rather than to the first electrode conductor, the ionization and glow discharge would occur at the second electrode conductor even through a voltage is applied to the second electrode conductor that is less than the voltage necessary initially to ionize discharge continues at successively narrower and narrower portions of the tapered conductor 30. Since there is no DC coupling across the gas or mixture of gasses but only AC coupling through the capacitance of the glass coversheets, each glow discharge is only momentary during each half-cycle of the AC voltage imthe gas in the absence of the collected charge. Therefore, the memory information represented by a glow discharge and the resultant collection of charge can be transferred from the first electrode conductor to the second electrode conductor.

Referring now to FIGS. 6 and 7, further to'illustrate this transfer phenomenon, a pair of planar glass sheets or-coversheets 31 and 32 define a neon-gas-filled space or envelope 34. Four electrode conductors 35, 36, 37, and 38 are affixed to the outer surface of the glass sheet 32. The electrode conductors 35, 36, 37 and 38 are placed very near to one another but are mutually separated or insulated from each other. A common electrode conductor 40 is affixed to the outer surface oftheglasssheet3l.

If a sufficiently high AC voltage is applied between the electrode conductors 36 and 40 by a voltage generator 41 that is electrically connected to the electrode conductors 36 and 40, a momentary glow discharge will occur at each half-cycle until sufficient charges collect in that half-cycle on the inner surfaces of theglass sheets 31 and 32 in the region around the electrode conductor 36 as shown generally by two clouds 42. The voltage that must be applied across the electrodes in order to initiate or ignite a glow discharge will vary with the area of the electrodes, the nature of the gas and its pressure, the nature and thickness of the glass coversheets and their separation, and the presence or absence of ambient ultraviolate light, etc. This might require, typically, 1,000 volts peak-to-peak. A wide range of AC frequencies is possible. A range of from 40 kilohertz to 300 kilohertz has proven convenient, but higher and lower frequencies are possible.

While the charges on the coversheets 31 and 32 are represented as a pair of clouds 42, it is to be understood that this charged state is similar to the state of charges in a parallel-plate capacitor.

Once a glow discharge occurs at the electrode conductor 36, the voltage generator 41 can reduce the AC voltage applied between the electrode conductors 36 and 40 to a value sufficient only to sustain a glow discharge typically between and 300 volts less,

depending upon the many parameters mentioned above.

These two clouds 42 of charge on the inside surfaces of the glass sheets 31 and 32 are shown extending beyond the edges of the electrode conductor 36. In fact, if the electrode conductors 35 and 37 are placed close enough to the electrode conductor 36, theclouds of charge 42 will extend partly into the regions of the electrode conductors 35 and 37.

If, under the conditions illustrated in FIGS. 6 and 7, and AC voltage of suitable magnitude such as approximately 700 volts peak-to-peak were subsequently applied to the electrode conductors 35 and 38 by a voltage generator 44, at a time when the AC voltage applied to the electrode conductor 36 is reduced suddenly by the voltage generator 41, to less than approximately 700 volts peak-to-peak, a glow discharge would momentarily occur between the electrode conductors 35 and 40. It must be defined, however, that this AC voltage applied to the electrode conductor 35 by the voltage generator 44 is of sufficient magnitude to cause a glow discharge to occur only when aided by the charges collected on the inside surfaces of the glass sheets 31 and 32 from a previous discharge. The polarity of the charge and the instantaneous polarity of the AC voltage must add to each other in order for discharge to occur. However, since the applied voltage is an AC voltage, the proper polarity in any case will soon occur after the application of the AC voltage. Also, this AC voltage must be of insufficient magnitude to cause a glow discharge to occur in the absence of collected charges from a previous glow discharge, for example at electrode 38.

ln this way, the memory phenomenon in the form of a collected charge under the electrode conductor 36 can be transferred to the electrode conductor 35 without generating a new cloud of charges at the electrode conductor 38. This occurs because the cloud of charge 42 that collects at the electrode conductor 36 extends over and aids in the generation of a glow discharge at the electrode conductor 35. However, the cloud of charges 42 is not wide enough to extend as far as the remote electrode conductor 38. In addition to its use as a visual display, this device can be used in a purely data-handling application. In such an application, the glow discharge phenomenon must be reduced to a purely electrical manifestation.

In order to sense the presence of a glow discharge on the electrode conductor 35, the current drawn from the voltage generator 44 can be sensed; or the electrode conductor 35 can be made of a transparent, conductive material, well known in the art; and a photocell 46 can be used to sense the glow discharge. As another alternative, an electrostatic probe conductor can be used to sense the charge resulting from a glow discharge.

It was mentioned that the glow discharge phenomenon is transferred from the electrode conductor 36 to the electrode conductor 35 by simultaneously increasing the AC voltage applied to the electrode conductor 35 and decreasing the AC voltage applied to the electrode conductor 36. There are many alternative ways of controlling these AC voltages to transfer this glow discharge. In order for transfer to occur, the transferee electrode conductor 35 must merely attain an instantaneous voltage sufiicient to generate a glow discharge before the transferor electrode conductor 36 reaches that instantaneous level of voltage.

Therefore, if a glow discharge occurs first at the transferee electrode conductor 35, it will rob the transferor electrode conductor 36 of its accumulated charge, thereby preventing the electrode conductor 36 from experiencing a glow discharge even though it might subsequently reach an instantaneous voltage equal to or even slightly exceeding thepeak voltage attained by the electrode conductor 35. Consequently, the transfer of a glow discharge or memory condition may even be accomplished by a phase change between the AC voltage applied to the electrode conductor 36 and the AC voltage applied to the electrode conductor 35.

Changing the phase between these AC voltages can be done by holding either AC voltage steady and retarding or advancing the other AC voltage. Or, one AC voltage could be advanced while the other is simultaneously retarded. This instantaneous voltage of the transferee electrode conductor 35 need only reach the necessary magnitude sooner than the transferor electrode conductor 36 in order to accomplish transfer.

Similarly, this same transfer result may be accomplished by adjusting the AC voltage levels, as mentioned previously. One AC voltage may be maintained or held constant and the other AC voltage may be decreased or increased. Or, one AC voltage may be decreased simultaneously with an increase of the other AC voltage.

In order to improve the transfer of a glow discharge, it may be desirable to use a combination of phase difference and voltage difference between the transferee electrode conductor and the transferor electrode conductor. That is, the AC voltage of the transferee electrode conductor'is both increased and advanced, while the AC voltage of the transferor electrode conductor is both reduced and retarded in order to transfer a glow discharge condition from the transferor electrode conductor to the transferee electrode conductor.

ln FIGS. 6 and 7, the electrode conductor 40 cooperates with both of the electrode conductors 35 and 36. However, the electrode conductor 40 could actually be two electrode conductors, one associated with the electrode conductor 36 and the other associated with the electrode conductor 35. Therefore, the voltage generator 41 could provide an AC voltage between one pair of electrode conductors, including the electrode conductor 36. The voltage generator 44 could provide an AC voltage between another pair of electrode conductors, including the electrode conductor 35.

TAPERED ELECT RODE SHIFT REGISTER It has been noted above in connection with FIGS. l-5, that, ignoring the charge collected on the inside surfaces of the glass sheets, the voltage existing at the inside surface of the glass sheet 22 is greatest adjacent to the center of the widest portion of the electrode conductor 30. Therefore, glow discharge will preferentially occur at that point.

Referring now to FIG. 8, a structure similar to FIGS. 6 and 7 is shown but with uniquely-shaped electrode conductors to cause a memory signal to change from one electrode conductor to another and back again in a controlled advance along both conductors. In FIG. 8,

the glass sheet32 is shown with the electrode conductor 36 acting as an ignition electrode. That is,when a signal is to be generated, a sufficient AC voltage is applied between the electrode conductor 36 and the common electrode conductor 40 (see FIG. 7) to cause a glow discharge inevitably to occur adjacent to the electrode conductor 36, without the aid of any charges that between and 50 cycles depending upon many factors may have collected on the insides of the glass sheets 31 v and 32 (see FIG. 7). This glow discharge causes charges to collect on the inside surfaces of the parallel glass sheets 31 and 32 adjacent to the electrode conductor 36 (FIG. 8). This charge distribution on the inside surfaces of the glass sheets 31 and 32 at the electrode conductor 36" is again represented by the cloud outline 42.

As previously explained, this cloud of charge 42 extends beyond the edges of the electrode conductor 36 and overlaps a portion of a nearby intermediate electrode conductor 50. The AC voltage applied to the electrode conductor 36 can then be reduced. If an AC voltage signal is applied to the electrode conductor 50, that is not of sufficient voltage to cause a glow discharge to occur unless aided by the charges of the cloud 42, no glow discharge will occur at the wide portion of the electrode conductor 50. However, since part of the cloud of charge 42 extends over a portion of the electrode conductor 50, that cloud of charge aids the voltage that is developed between the electrode con ductor S0 and the common conductor 40 (FIG. 7). On the occurrence of the proper polarity and magnitude of AC voltage signal at the electrode conductor 50 coupled with a significant reduction or retardation of the AC voltage applied to the electrode conductor 36 a glow discharge will occur in the region where the cloud ductor 50.

As mentioned. previously, a glow discharge preferentially occurs at the wider portion of an electrode conductor since the field at the center of a wide portion of the conductor is greater than the field at a narrow portion of the conductor. Consequently, at each successive cycle of the AC voltage signal that is applied to the electrode conductor 50, the glow discharge phenomenon migrates from the narrow end of the conductor 50 to the wider end at the right of the electrode conductor 50. This has been found to require of charge 42 overlaps a portion of the electrodecon- I including the size of the electrode conductor and the degree of its taper as well as the magnitude of the applied AC voltage.

If sufficient voltage were applied to the electrode conductor 50, a glow discharge could occur over its entire area. However, not enough voltage is applied for that to occur, and a glow discharge only occurs at the widest area of the electrode conductor 50 since a charge cloud resulting from the glow discharge at th'e wide end of the electrode conductor 50 tends to overlap the narrow end of the electrode conductor 50 and inhibit discharge at that narrow end in the absence of significantly higher voltage.

While it may notbe essential, it is preferred that the glow discharge condition always be maintained at the electrode conductor 36. Therefore, the AC voltage applied to the electrode conductor 50 is normally main tained so as to prevent the transfer of a glow discharge condition from the electrode conductor 36. However, when a glow discharge condition is desired for purposes to be discussed subsequently, the AC voltage on the electrode conductor 50 can be controlled so as to transfer a glow discharge condition from the electrode conductor 36.

This glow discharge at the electrode conductor 50 deposits its own cloud of charge 52 on the inside surface of the glass sheet 31 and 32. Sufficient voltage is applied to the electrode conductor 50 to cause the cloud of charge 52 to'overlap the narrow end of another electrode conductor 54 which has. a tapered shape similar to the electrode conductor 50. Therefore, a subsequent AC voltage signal of comparable magnitude applied to the electrode conductor 54 accompanied by a reduction in the AC voltage applied to the .electrode conductor 50 causes a glow discharge to occur at the electrode conductor 54 where it is overlapped by the cloud of charge 52. The occurrence of a glow discharge at the narrow end of the electrode conductor 52 takes charges from the wide endof the electrode conductor 50 and starves the electrode conductor 50 of its charge cloud 52. The glow discharge in the region adjacent the electrode conductor 54 draws the collected charges away from much of the area of the electrode conductor 50.

In the same manner that is described in connection with the electrode conductor 50, successive cycles of the AC signal applied to the electrode conductor 54 cause the glow discharge to migrate to the wider portion of the electrode conductor 54 and to deposit clouds of charge of alternating polarity on the inside surfaces of the glass sheets 31 and 32 in a pattern substantially as shown by the outline 62 in FIG. 8.

I It can be seen that this cloud of charge 62 overlaps another tapered electrode conductor 64. If an AC signal is applied to the electrode conductor when the AC signal applied to the electrode 54 is reduced, a glow discharge will occur at the portion of the conductor 64 that is overlapped by the cloud 62. The occurrence of a glow discharge at the electrode conductor 64 draws charge from the cloud 62, starving the electrode conductor 54 of its charge of favorable polarity. This causes the glow discharge at the electrode conductor 54 to be extinguished even though an AC voltage signal is still applied to the electrode conductor 54. The

remainder of the cloud 62 of charge quickly dissipates under these conditions. Continued application of an AC voltage signal on the electrode conductor 64 causes the glow discharge on the electrode conductor 64 to migrate to the wide end of the electrode 64, as represented by the charge cloud 66.

It can be appreciated that a binary bit of information generated at the electrode conductor 36 can be transferred to the electrode conductor 50. By alternations of the amplitude of magnitude of the AC voltage signals applied to the electrode conductors 54 and 64, this bit of information can be advanced to the right in FIG. 8. This bit of information is thus moved from one set of electrodes 54 to the other set of electrodes 64, and back again, in the form of a glow discharge.

Referring now to FIG. 9 there is shown a series of interconnected shift registers that can be mounted on the same glass sheet 32. In order to introduce the binary bit of infomiation, a sufficiently high AC voltage is applied between the igniting electrode conductor 36 and a common electrode conductor 40 (now shown in FIG. 9). This glow discharge is then transferred to an intermediate electrode conductor 50 and subsequently to an electrode conductor 54 having several segments on it designated by the numbers 54-1, 54-2, etc. The glow discharge can then be transferred from the electrode conductor segment 54-1 to the first segment 64-1 of the companion to electrode conductor 64, having several segments 64-1, 64-2, etc. Therefore, this signal or binary bit in the form of a glow discharge can be transferred from the electrode conductor segment 54-1 to the electrode conductor segment 64-1 and back to the electrode conductor 54 but on the segment 54-2 and then to the electrode conductor segment 64-2, etc., as far to the right as possible, as shown in FIG. 9. The several segments of the electrode conductors 54 and 64 together form a shift register.

A plurality of orthogonal electrode conductors 67, 68, 69 and 70 are electrically connected to the electrode conductor 64 and thus experience the same AC voltage signals that are applied to the electrode conductor 64. A plurality of independent electrode conductors 72, 74, 76 and 78 are arranged substantially parallel to the electrode conductors 67, 68,69 and 70. The electrode conductors 72 and 67 together form another shift register. Similarly, the electrode conductors 74 and 68 together form a shift register. The same is true with the electrode conductors 76 and 69 and with the electrode conductors 78 and 70.

When a glow discharge is maintained at the electrode conductor segment 64-1, it can readily be transferred to the first segment 72-1 of the electrode conductor 72. It can be observed in FIG. 8 that the cloud 66 overlaps the narrow end of the tapered electrode conductor segment 72-1. Ignition of a glow discharge at the electrode conductor 72-1 draws the charges away from the electrode conductor segment 64-1, which causes the electrode conductor segment 64-1 to cease its glow discharge.

The binary bit signal represented by the glow discharge can then be held at the electrode conductor segment 72-1 and is moved to its wider end by continued AC voltage excitation of the electrode conductor 72, while an additional binary bit signal is transferred from the firing electrode conductor 36 to the interrnediate electrode 50. When the additional signal is transferred from the segment 54-1 to the segment 64-1, the previous signal at the segment 72-1 is transferred to the segment 67-1. The additional signal can then be transferred to the segment 54-2 and so forth down the shift register comprising the electrode conductors 54 and 64.

It may later be desired to transfer that latter additional binary bit signal of information to one of the orthogonal electrode conductors, for example the electrode conductor 76. At the proper time, an AC voltage signal of the proper magnitude is applied to the orthogonal electrode conductor 76. This proper time occurs when the bit signal is at the electrode conductor segment 64-3. The additional binary bit signal is thus transferred to the electrode 76-1. Similarly, once the glow discharge bit has been transferred to the first segments of the electrode conductors 72, 74, 76 or 78,

they can be transferred along their associated, orthogonal shift registers in the same manner that they could be transferred along the shift register comprising the electrode conductors 54 and 64.

Since the manifestation of the data in the shift registers as shown in FIGS. 8 and 9 is a visible glow discharge, the display characteristic of these shift registers is evident to one of ordinary skill in the art.

However, in order to use these devices as data shift registers, the data must be sensed at predetermined points and at predetermined times in order to ascertain whether or not a glow discharge occurs at any given electrode conductor segment. This can be accomplished, for example, by a properly-positioned photocell as describedand shown in connection with FIGS. 6 and 7.

Alternatively, a sensing electrode conductor 77 can be placed on the glass coversheet 32. A bit sensor 79 can then be connected to the sensing electrode conductor. If a glow discharge occurs at the adjacent electrode conductor segment 72-3, a charge cloud near the wide end of the electrode conductorsegment 72-3 will overlap the sensing electrode conductor 77. The glow discharge can then be transferred to the sensing electrode conductor 77 by a voltage generator contained in the bit sensor 79 by the technique described above. The current sent to the sensing electrode conductor 77 by the bit sensor 79 can then be measured to determine whether or not there actually was a bit of data transferred from the electrode conductor segment 72-3 to the sensing electrode conductor 77. Once measured,

the data bit can be transferred back to the electrode conductor segment 72-3.

As still another alternative, a charge sensor such as a field-effect transistor could-be used to sense the charge over-lapping the, sensing electrode conductor 77 from the electrode conductor segment 72-3 in the presence of a glow discharge.

In connection with FIGS. 6, 7, 8 and 9 it has been previously mentioned that there is a common electrode conductor 40 that is placed on one glass sheet 31 and that all the AC voltage signals applied to the electrode conductors on the other glass sheet 32 are sinusoidal or AC voltage signals with respect to the electrode conductor 40. It will be recognized that a glow discharge is maintained at any one electrode conductor or electrode conductor segment by the presence of an AC sufficient magnitude when added to the collected charge to cause the gas to ionize, but this magnitude is inadequate to cause ionization without that collected charge.

In the case of two adjacent electrode conductors, such as the electrode conductors 54 and 64 of FIG. 9, a glow discharge will remain at the electrode conductor segment 54-1 and will not transfer to the electrode conductor 64-1 so long as the AC voltage applied to the electrode conductor 54 is greater than the AC voltage applied to the, electrode conductor 64. Conversely, when the AC voltage that is applied to the electrode conductor 64 becomes sufficiently greater than the AC voltage applied to the electrode conductor 54, the volt age across the gas between the glass sheets rises faster under the electrode conductor 64 than it does under the electrode conductor 54. Therefore, the glow discharge will occursooner under the electrode conductors 64 than it will occur under the electrode conductor 54. In fact, the occurrence of a glow discharge under the electrode conductor segment 64-1 will dissipate all of the charge or a sufficient quantity of the charge previously existing under. the electrode conduc tor segment 54-1 to starve the electrode conductor segment 54-1 of charge and thus extinguish the glow discharge under the electrode conductor segment S41. Therefore, a significant change in voltage between the electrode conductors 54 and 64 will cause the glow discharge condition to transfer from one electrode conductor to the other electrode conductor.

The important consideration in this transfer of the glow discharge condition is not so much the absolute magnitude of the AC voltage applied to an electrode conductor on the glass sheet 32 but relates principally to the relationship between the voltages applied to the electrode conductors 64 and 54. The only requirement of the absolute magnitude of the AC voltage level is that the higher of the two voltage levels must have a peak voltage sufficient to cause a glow discharge to occur in the presence of a collected charge field, and the higher of the two voltage levels must not have a peak voltage sufiicient to cause a glow discharge to occur in the absence of a collected charge cloud or field. It has been found that a significant range of acceptable AC signal voltages is possible, typically, between and 300 volts, depending upon the nature, pressure, and other characteristics of the gas existing between the two glass sheets, the nature, the thickness and the separation of the glass sheets, and the areas of the electrode conductors and their separation from one another.

Since the electrode conductors 64, 67, 68, 69 and 70 the voltage of the electrode conductor 64, glow' discharge signals present on the electrode conductor 54 will be transferred to the electrode conductor 64 from the wide ends of the segments of the electrode conductor 54 to the narrow ends of the next adjacent segments of the electrode conductor 64. Similarly, when the AC voltage of the electrode conductor 54 is raised significantly above the AC voltage of the electrode conductor 64, the glow discharge signals present on the various segments of the electrode conductors'64 will transferred to the segments of the electrode conductor 54 that are to the right of the corresponding segments of the electrode conductor 64.

Alternatively, any glow discharge occurring or existing on the electrode conductor. 64 at such time as one of the orthogonal electrode conductors 72, 74, 76 or 78 is raised to a voltage significantly above the AC voltage of the electrode conductor 64, will be transferred to the first segment of the orthogonal electrode conductor 72, 74, 76 or 78. Therefore, that glow discharge condition of the associated segment of the electrode conductor 64 will be extinguished from the segment of the electrode conductor 64 by the presence nearby of the higher voltage and resultant early glow discharge to draw the charges away from the associated segment of the electrode conductor 64. It will be apparent that the electrode conductors 72, 74, 76 and 78 can be controlled separately as mentioned above or can be electrically interconnected.

ALTERNATIVE SHIFT REGISTER As has been mentioned above, the arrangement of FIG. 9 presupposes a common electrode conductor 40 opposite the electrode conductors shown in FIG. 9. However, FIG. 10 show an alternative embodiment of the present invention in which patterned electrodeconductors are arranged on both sheets of glass. The conductors represented in FIG. 10 by light outlines and cross-hatch lines are attached to one sheet of glass and the electrode conductors represented by bold object lines and no cross hatching are mounted on the opposite sheet of glass. The AC'voltages applied to the several electrode conductors on one sheet of glass in FIG. 10 are referenced to the electrode conductors on the other sheet of glass in FIG. 10 rather than to a common electrode conductor.

As an example of the operation of the array of FIG. 10, assume that a high AC voltage signal is applied to the electrode conductor 80 while a low AC voltage is applied to the electrode conductor 82. At the same time assume that a high AC voltage is applied to the orthogonal electrode conductors 84 and 86, but assume that a low AC voltage is applied to the electrode conductor 88. In addition, assume that a glow discharge is initially present between the electrode con-,,

ductors 84 and 80. The high AC voltages that are applied between the electrode conductors 80 and 84 must be in the proper phase to add their peak voltages of opposite polarity to generate a peak voltage in the area where they overlap.

Since the voltage on the electrode conductor 82 is lower than the voltage on the electrode conductor 80, a lower voltage exists between the electrode conductors 82 and 84 than exists between the electrode conductors 80 and 84. Similarly a lower voltage exists between the electrode conductors 80 and 88 than exists between the electrode conductors 80 and 84. Therefore, as shown in FIG. 10, the glow discharge will remain in the region between the electrode conductors 80 and 84.

If at this point, the voltage of the electrode conduc tor 80 is reduced significantly and the AC voltage of the electrode conductor 82 is raised significantly, the glow discharge will transfer from the position between the electrode conductors. 80 and 84 to the position between the electrode conductors 82 and 84 assuming that the electrode conductors 84 and 86 are maintained at a high AC voltage and the electrode conductor 88 is maintained at a low AC voltage. When the voltage of the electrode conductor 88 is subsequently increased significantly and the voltage of the electrode conductors 84 and 86 is reduced significantly, with no change in'the high voltage at the electrode conductor 82 and the low voltage at the electrode conductor 80, the glow discharge will transfer from the region between the electrode conductors 82 and 84 to the region between the electrode conductors 82 and 88. Therefore, it can be seen that a glow discharge can advance from one position to the next by controlling the AC voltages existing between the conductors on opposite sheets of glass.

Continuing with the advance of the glow discharge presently existing between the electrode conductors 82 and 88, significant increase in the voltage applied to the electrode conductor 80 accompanied by a significant decrease of the voltage at the electrode conductor 82 causes the glow discharge to transfer to the position between the electrode conductor 88 and the electrode conductor 80. Subsequent lowering of the voltage at the electrode conductor 88 accompanied by an increased AC voltage on the electrode conductors 84 and 86 causes the glow discharge to advance to the position between the electrode conductor 86 and the electrode conductor 80.

Although the electrode conductor 84 has the same voltage as the electrode conductor 86, the glow discharge will not transfer directly from the electrode conductor 88 to the electrode conductor 84 in the example explained above; because, the electrode conductor 80 is rather narrow in the region between the electrode conductor 84 and the electrode conductor 88 and is rather wide in the region between the electrode conductor 88 and the electrode conductor 86. In addition, the electrode conductor 88 is very close to the electrode 86 in the region adjacent the electrode conductor 80. Whereas, the electrode conductor 88 is rather far from the electrode conductor 84 in the region of the electrode conductor 80.

It can be seen that by reversing the order of increases and decreases of the voltages of the various electrode conductors, the glow discharge can be stepped in the reverse direction. For example, assume that the glow discharge exists between the electrode conductors 80 and 88. A lowering of the voltage of the electrode convoltage of the electrode conductor 88 causes the glow discharge to move to the area between the electrode conductors 82 and 84.

Referring now to FIG. 1 1, there is shown an arrangement of the electrode conductors similar to FIG. but arranged to transfer a glow discharge along a leg 89 of a shift register 90 and back down another leg 91 of the shift register 90 that is folded over the leg 89. Four ductor 80 accompanied by the raising of the voltage of electrode conductors 92, 93, 94 and 96 are arranged parallel to each other on the outer surface of one of two glass sheets forming the envelope of gas. The electrode conductors 92 and 94 experience the same AC voltage. Electrode conductors 93 and 96 experience the same AC voltage. The electrode conductors 92 and 94, however, experience different AC voltages than the electrode conductors 93 and 96. When a high AC voltage is applied to the electrode conductors 92 and 94, a low AC voltage is applied to the electrode conductors 93 and 96. Similarly, when a'low AC voltage is applied to the electrode conductors 92 and 94, the electrode conductors 93 and 96 experience a high AC voltage.

An ignition electrode 98 is placed on the other sheet of glass and is always supplied with sufficient AC voltage with respect to the electrode conductor 92 or the electrode conductor 93 to cause a glow discharge to occur in the region between the ignition electrode conductor 98 and the electrode conductor 92 or the electrode conductor 93, no matter what the previous state of this region was. This function is similar to the ignition electrode 36 of FIG. 8; therefore, a glow discharge is always available for transfer to a first intermediate electrode conductor 100. The first intermediate electrode 100 is sometimes maintained at a low AC voltage and sometimes a high AC voltage.

When the first intermediate electrode conductor 100 is maintained at a high AC voltage, a glow discharge will transfer from the ignition electrode conductor 98 to the first intermediate conductor 100 along the electrode conductor 92 in the region where the electrode conductors 98 and 100 are closer to each other. When the voltage of the electrode conductor 92 is subsequently decreased and the voltage of the electrode conductor 93 is increased, the glow discharge adjacent the first intermediate electrode conductor 100 then transfers from the area where the electrode conductor 92 overlaps the first intermediate electrode conductor 100 to the region where the electrode conductor 93 overlaps the first intermediate electrode conductor 100. Therefore, when the voltages on the electrode conductors 100 and 93 are high, a glow discharge condition is always available between them.

A second intermediate electrode conductor 102 is positioned adjacent the first intermediate electrode conductor 100 along the length of the electrode conductor 93. The second intermediate electrode conductor 102 isnormally maintained at a very low AC voltage such that a glow discharge will not ordinarily be transferred from the first intermediate electrode conductor 100 to the second intermediate electrode conductor 102 in the region adjacent the electrode conductor 93. However, when it is desired that a glow discharge should be transferred along the shift register 90, the AC voltage of the second intermediate electrode conductor 102 is raised to a higher AC voltage with respect to the electrode conductor 93. This higher transferred from the first intermediate electrode conductor 100 to the second intermediate electrode 102 while the electrode conductor 93 is maintained at a high electrode AC voltage and the electrode conductor 92 is maintained at a low AC voltage.

The second intermediate electrode conductor 102 will then be maintained at a high AC voltage while the voltage on the electrode conductor 93 is reduced and the voltage on the electrode conductor 92 is increased to cause the glow discharge condition to step from the area where the second intermediate electrode conductor 102 overlaps the electrode conductor 93 to the region where the second intermediate electrode conductor 102 overlaps the electrode conductor 92. At this point, successive changes of the voltage applied to the electrode conductors 92 and 93 and to the electrode conductors that are on the same glass sheet as the electrode conductors 98, 100 and 102 cause the glow discharge condition to advance along the first leg 89 of the shift register 90 in the same manner as was explained in connection with FIG. 10.

When the glowvdischarge condition reaches the region where an electrode conductor 110 overlaps the electrode conductor 93, a reduction in the voltage of the electrode conductor 110 is accompanied by an increase in the voltage of two other electrode conductors I12 and 114. This causes the glow discharge condition to advance to the region where the electrode conductor 114 overlaps the electrode conductor 93. When the voltage on the electrode conductors 93 and 96 is reduced and the voltage on the electrode conductors 92 and 94 is increased, this glow discharge condition is transferred along the electrode conductor 1 14 from the region adjacent the electrode conductor 93 to the region adjacent the electrode conductor 94. Meanwhile, the electrode conductor 1 14 is still maintained at a high AC voltage. Subsequently, the AC voltage on the elec trode conductors '1 12 and 114 is reduced, accompanied by an increase in the AC voltage of the electrode conductor 1 10. The voltage of the electrode conductor 94 remains the same. This causes the glow discharge condition to be transferred to the region between the electrode conductors 1 l and 94.

Successive alterations of the AC voltages applied to the various electrode conductors similarly causes the glow discharge condition to migrate to the left along the leg 91 of the shift register 90 until it reaches the region between a transfer electrode conductor'120 and the electrode conductor 96. The glow discharge condition can then be transferred along the electrode conductor 120 to another electrode conductor 122 of an adjacent shift register very similar to the shift register 90. The electrode conductor 122 would correspond to the electrode conductor 92 of the shift register 90. The adjacent shift register would then have no need of the electrode conductors 98, 100, and 102.

It will be apparent to one of ordinary skill in the art that several of these folded shift registers such as the shift register 90 can be arranged in succession and that glow discharges can selectively be inserted into the end shift register by the electrode conductors 98, 100, and 102 or even by another shift register and can be transferred sinuously along a plurality of these shift registers to form a glow discharge display or a large-capacity electronic storage system.

Referring now to FIG. 12, an alternate embodiment is shown of the shift register of FIG. 10 in which hits of information can selectively be inserted at various points along the length of the shift register and can then be transferred to an orthogonal shift register. A first shift register 130 is shown, very much like the shift register of FIG. 10. An ignition or firing electrode conductor 132 is positioned on one of the glass sheets. A companion ignition electrode conductor 134 is positioned on the opposite glass sheet. The electrode conductors 132' and 134 have a plurality of ignition pads 135 which are arranged in an arbitrary, predetermined pattern adjacent the shift register 130. A glow discharge is ignited at all of the pads 135 by a high AC voltage applied between the electrode conductors 132 and 134. This high AC voltage is then reduced to the normal maintaining voltage. The voltage of an electrode conductor 136 of the shift register 130 is then increased and the voltage of a parallel electrode conductor 138 of the shift register 130 is decreased at the same time that a high AC voltage is maintained on a plurality of electrode conductors 140 that run perpendicular to the electrode conductors 136 and 138. At this time the voltage between the ignition electrode conductors 132 and 134 is sharply reduced so that the glow discharge conditions that had existed on the pads. 135 between the electrode conductors 132 and 134 are transferred to the regions between the electrode conductor 136 and the electrode conductors 140. However, a glow discharge will be transferred only to those regions of the shift register 130 which are adjacent to the selectively arranged ignition pads 135 of the electrode conductors 132 and 134. In order to form an alphanumeric display, it will be apparent that the ignition pads of the electrode conductors 132 and 134 would be arranged in accordance with the locations of dots necessary to form the alphanumeric or other characters of the display.

The glow discharge conditions existing on the shift register 130 can then be transferred to the right along the shift register 130 in the manner that is described in connection with the shift register of FIG. 10. When a glow discharge condition reaches the area designated by the reference number 142, it can be transferred to an orthogonal shift register 144 at such time as the adjacent region referred to by the reference number 146 is experiencing a high AC voltage. This glow discharge condition can then be carried along the shift register 144 in the manner described in conjunction with FIG.

Referring now'to FIG. 13, an entire encoding and display system is shown schematically using many repetitions of the folded shift register disclosed in FIG.

11 as the actual., display screen 150. The shift register 144 from FIG. l2iis arranged perpendicular .to a plurality of shift registers -A, 130-B, 130-C, etc., similar to the shift register 130 of FIG. l2. A plurality of ignition electrode conductors 132-A, 132-B, 132-C, etc., are arranged similar to the ignition electrode conductors 132 and 134 of FIG. 12. The dash letters are used in FIG. 13 to represent the alphanumeric character associated with each of the ignition electrode conductors 132 and each of the shift registers 130.

As an example of the operation of the display system of FIG. 13, to display the letter A a high AC voltage is appliedto the ignition electrode conductor 132A.

The glow discharge conditions generated at the ignition pads of the electrode conductor 132-A are then transferred to the shift register 130-A as explained in connection with FIG. 12. The glow discharge conditions then existing in the shift register 130-A are transferred to the right in FIG. 13 and onto the orthogonal shift register 144 which carries the glow discharge conditions to the display screen 150. At the display screen 150 the glow discharge conditions are carried from segment to segment of the display screen 150 as explained in connection with FIG. 11; Naturally, the glow discharges in the display screen 150 are advanced rapidly until they are in position for an intelligible display, at which time the advance is stopped momentarily to permit visual perception of the display.

If the next character to be displayed is the letter B, a high AC voltage is applied to the ignition electrode conductor 132-B. These glow discharge conditions are then transferred to the shift register 130-8 and are carried along to the shift register 144. It will be noted that the ignition electrode conductor 132-8 extends further to the right in FIG. 13 than does the ignition electrode conductor l32-A. This is to accommodate the displacement of the shift registers 130 along the length of the shift register 144. Three complete shift register elements along the shift register 144 are located between each adjacent shift register 130. Therefore, each ignition electrode conductor 132 for each successive alphanumeric character that is placed further away from the display panel 150 should also be placed threeshift-register-elements to the right of the adjacent ignition electrode conductors 132. Each alphanumeric character to be displayed may require precisely the same number of shift register cycles to reach the same spot on the display screen 150 from the instant of ignition at its associated ignition electrode conductor 132.

Although various specific embodiments of the invention are shown in the drawings and described in the foregoing specification, it will be understood that in,- vention is not limited to the specific embodiments described, but is capable of modification and rearrangement and substitution of parts and elements without departing from the spirit of the invention.

What is claimed is:

1. An apparatus wherein a plasma discharge occurs in a gas-filled, dielectric envelope by applying an AC. voltage between two electrodes on opposite sides of the envelope, characterized by one of the electrodes being tapered with the plasma discharge being applied first near the narrow end of the tapered electrode and progressing in steps toward the wide end on each halfcycle of the applied AC. voltage which causes a greater capacitive coupling through the dielectric envelope at wider portions of the tapered electrode causingdischarge to preferentially occur near the wide end of the electrode.

2. In a plasma discharge device of the type having a gas sealed in a confined envelope area between a pair of dielectric coversheets, each coversheet having conductors thereon with the conductors being located opposite one another across the gas-filled space, so that ionization of the gas takes place when a predetermined voltage exists across the space between the conductors causing the gas to glow, an improvement including:

the dielectric envelope being of a size capable of supporting a plurality of simultaneous glow discharges; means for applying voltage to the conductors; and the shape of the gas filled envelope relative to the shape of at least one of the conductors being such that the area of the gas filled space beneath the conductor varies in a predetermined manner along at least one conductor, so that the application of voltages of different magnitude by the voltage applying means causes discharges to take place in different portions of the envelope corresponding .to a predetermined relationship of applied voltage to the gas filled area beneath the electrodes. 3. An improved apparatus for display or memory, having a first and second dielectric coversheet spaced apart and sealed to form an envelope with a gas therein and at least one conductor on the first coversheet outside of the envelope and at least two conductors on the second coversheet outside of the envelope, means for selectively initiating a glow discharge in the gas between the conductor on the first coversheet and one of the conductors on the second coversheet, and means for continuously applying AC voltage between the conductor on the first coversheet and the conductors on the second coversheet, the AC voltage being of insufficient magnitude to initiate a glow discharge but of sufficient magnitude to sustain a glow discharge, wherein theimprovement comprises:

means for causing the AC voltage on the one of the conductors on the second coversheet to be reduced relative to the AC voltage on the other of the conductors on the second coversheet, thereby causing the glow discharge condition to migrate from between the one conductor on the second coversheet and the conductor on the first coversheet to between the other conductor on the second coversheet and the conductor on the first coversheet.

4. An improved apparatus for display or memory, having first and second dielectric coversheets spaced apart and sealed to form an envelope with a gas'therein and at least one conductor on the first coversheet outside of the envelope and at least a first conductor and a second conductor on the second coversheet outside of the envelope, means for selectively initiating a glow discharge in the gas between the conductor on the first coversheet and the first conductor on the second coversheet, and means for continuously applying an AC voltage between the conductor on the first coversheet and the first and second conductors on the second coversheet, the AC voltage being of insufficient magnitude to initiate a glow discharge but of sufficient magnitude to sustain a glow discharge, wherein the improvement comprises:

means for changing the AC voltage applied between the first conductor on the second coversheet and the conductor on the first coversheet relative to the AC voltage applied between the second conductor on the second coversheet and the conductor on the first coversheet to cause the instantaneous voltage applied to the second conductor on the second coversheet to reach the magnitude sufficient to maintain a glow discharge sooner than the instantaneous voltage applied to the first conduccoversheet. 7

"voltage applied to the first conductor on the second cover-sheet relative to the AC voltage applied to the second conductor on the second coversheet while continuing to maintain the relatively reducedvAC voltage at a magnitude sufficient to sustain a discharge.

6. An apparatus according to claim wherein the 15. An apparatus according to claim 14 wherein the second conductor is one of a plurality of electricallyconnected, generally tapered electrode segments arranged in a line on the second coversheet;- and wherein the first conductor is one of a plurality of electrically-connected, generally tapered electrode segments arranged in a line on the second coversheet.

16. An apparatus according to claim 15 wherein the wide ends of the taperedelectrode segments of the first conductor are positioned adjacent but not touching the reducing means comprises means for holding constant the AC voltage applied to the first conductor on the second coversheet and means for increasing the AC voltage applied to the second conductor on the second 7. An apparatus according to'claim 5 wherein the reducing means comprises means for holding constant the AC voltage'applied to the second conductor on the second coversheet and means for decreasing the AC narrow ends of the tapered electrode segments of the second conductor, and thezwide ends of the tapered electrode segments of the second conductor are positioned adjacent but not touching the narrow ends-of the tapered electrode segments of the first conductor.

17. An apparatus according to claim 16 further com- 1 prising'a third conductor on the second coversheet voltage applied to the first conductor on the second of the AC voltages to cause the instantaneous voltage applied to the second conductor on the second coversheet to rise sooner than the instantaneous voltage, applied to the first conductor on the second coversheet. g

10. An apparatus according to claim 9 wherein the varying means comprises means for holding steady the AC voltage applied to the first conductoron the second coversheet and means for advancing the AC voltage applied to the second conductor on the second coversheet.

11. An apparatus according to claim 9 wherein the varying means comprises means for holding steady the AC voltage applied to the second conductor on the second coversheet and means for retarding the AC voltage applied to the first conductor on the second coversheet.

12. An apparatus according to claim 9 wherein the varying means comprises means for retarding the AC voltage applied to the first conductor on the second coversheet andmeans for advancing the AC voltage applied to the second conductor on the second coversheet.

13. An apparatus according to claim 4 wherein at least the second conductor on the second coversheet is generally tapered, having a narrow end and a wide end.

14. An apparatus according to claim 13 wherein the conductors on the second coversheet are positioned with the narrow end of the tapered second conductor adjacent but not touching the first conductor.

positioned adjacent the wide end of one of the tapered segments on the second coversheet and means for transferring a glow discharge condition from-the one tapered segment to the third conductor;

the third conductor being tapered, having a wide end and a narrow end, with the narrow end of the third conductor positioned adjacent to but not touching the one tapered segment; and

thethird conductor being one of a plurality of electrically connected, generally tapered electrode segments arranged in a line perpendicular to the lines of the first and second conductors.

18. An apparatus according to claim 17 further comprisinga plurality of fourth tapered, electrically-connected conductors on the second coversheet arranged in a line parallel with the line of thethird conductor; and i the fourth conductors being electrically connected to one of the other conductors on the second coversheet. I I

19. A shift register for moving data bits generally in a line comprising: v

a dielectric, gas-filled envelope having two sides;

a first pair of conductors on the outside of one side of the envelope, extending parallel to each other and generally along the line; a r

a plurality of orthogonal conductors on the outside of the envelope and on the other side of the envelope and extending generally perpendicular to the first pair of conductors;

a plurality of ignition electrodes selectively arranged in a row on the outside of the envelope parallel with the line;

means for applying an AC voltage to the ignition electrodes, the magnitude of the AC voltage being sufficient to initiate a plasma discharge at each ignition electrode and within the envelope;

means for applying AC voltage between at least one of the first pair of conductors and at least one of the orthogonal conductors, the magnitude of AC voltage being sufficient to sustain a plasma discharge but insufiicientto initiate a plasma discharge; and

means for controlling the AC voltage applied to the conductors for causing the plasma discharge to progress between the first pair of conductors and the orthogonal conductors generally along the line.

20. A shift register according to claim 19 further comprising a second shift register arranged generally in a second line intersecting the line of the first shift register and arranged so that a bit-representing plasma discharge progressing along the line on the first shift register is transferred to the second shift register and progresses along the secondline on the second shift register.

21. A shift register according to claim 19 further comprising:

a second pair of conductors on the outside of the envelope cooperating with the orthogonal conductors and extending parallel with the first pair of conductors with each conductor of the second pair of conductors associated with a corresponding oneof the first pair of conductors; andmeans for receiving a plasma discharge from the first pair of conductors and in response thereto for initiating progression of the plasma discharge on the second pair of conductors generally along a second line parallel with the line of the first pair of conductors comprising a shift register folded on itself.

22. A display device comprising:

a dielectric, gas-filled envelope;

a plurality of shift registers comprising conductors on the outside of the envelope for moving data-bitrepresenting plasma discharges generally along substantially parallel lines;

means associated with each shift register for selectively initiating plasma discharges in the shift registers;

a manifold shift register arranged along a line intersecting the parallel lines for receiving plasma discharges from the shift registers and for moving the plasma discharges generally along the intersecting line; and

means for receiving plasma discharges from the manifold shift register and for visually displaying the plasma discharges.

23. A method of controlling a memory condition at a first location between a first pair of electrical conductors and at a secondlocation between a second pair of electrical conductors, a first conductor of the second pair of conductors being tapered with the narrow end of the tapered first conductor being positioned adjacent but not touching a first conductor of the first pair of conductors, no more than a single conductor of the first pair of conductors being in common with no more than a single conductor of the second pair of conductors, comprising the steps of: I

applying an AC voltage between the first pair of electrical conductors of a magnitude sufficient to maintain the memory condition at the first locaapplying an AC voltage between the second electrical conductors;

causing the instantaneous voltage applied to the second pair of electrical conductors to reach the magnitude sufficient to maintain a memory condition sooner than the instantaneous voltage applied to the first pair of electrical conductors reaches the magnitude sufficient to maintain a memory condition, thereby causing the memory condition to move to the second location from the first location; and

pair of continuing the application of AC voltage between the second pair of electrical conductors, thereby causing the memory condition to migrateto the wide end of the tapered first conductor.

24. A method of controlling a memory condition at a first location between a first pair of electrical conductors and at a second location between a second pair of electrical conductors, no more than one conductor of the first pair of conductors being in common with no more than one conductor of the second pair of conductors, comprising the steps of:'

applying an AC voltage between the first pair of electrical conductors of a magnitude sufficient to maintain the-memory condition at the first location; I

applying an AC voltage between the second pair of electrical conductors; and causing the instantaneous voltage applied to the second pair. of electrical conductors to reach the magnitude sufficientto maintaina memory condition sooner than the instantaneous voltage applied to the first pair of electrical conductors, thereby causing the memory condition to move to the second location from the first location.

25. A method according to claim 24 wherein the causing step comprises reducing the magnitude of the AC voltage applied between the first pair of conductors with respect to the AC voltage applied between the second pair of conductors so that the magnitude of the AC voltage between the first pair of conductors is less than the magnitude of the AC voltage between the second pair of conductors but still sufficient to maintain a memory condition.

. 26. A method according to claim- 25 wherein the reducing is accomplished by holding constant the AC voltage applied between the first pair of conductors and increasing the AC voltage applied between the second pair of conductors.

27. A method according to claim 25 wherein the causing step further comprises varying the phase of the AC voltages simultaneously with reducing themagnitude of the AC voltage applied between the first pair of conductors with respect to the second pair of conductors to cause the voltage applied between the second pair of conductors to rise sooner than the voltage applied between the first pair of conductors.

28. A method according to claim 24 wherein the causing step comprises varying the phase of the AC voltages to cause the instantaneous voltage applied between the second pair of conductors to rise sooner than the instantaneous voltage applied between the first pair of conductors.

29. An improved method of controlling a display or memory device having first and second dielectric an AC signal to the first and second conductors,

means for applying an AC voltage to the third and coversheet which AC voltage difference has a maximum magnitude equal to the sum of the peak-to-peak voltages of the AC voltages applied to the conductors on the two coversheets, the maximum magnitude of the AC voltage difference between the conductors on the first coversheet and the conductors on the second coversheet being of insufficient magnitude to initiate a glow discharge in the gas but of sufficient magnitude to sustain a glow discharge in the gas, wherein the improved method comprises:

controlling the AC voltages applied to the first and second conductors so that the instantaneous voltage difference between the first conductor and at least one of the I conductors on the second coversheet reaches an instantaneous magnitude sufficient to sustain glow discharge in the gas sooner than the instantaneous AC voltage applied between the second conductor and the conductors on the second coversheet reaches an instantaneous magnitude sufficient to sustain a glow discharge in the gas; controlling the AC voltages applied to the third and fourth conductors so that the instantaneous voltage difference between the third conductor and at least one of the conductors on the first coversheet reaches an instantaneous magnitude sufficient to sustain a glow discharge in the gas sooner than the instantaneous AC voltage applied between the fourth conductor and the conductors on the first coversheet reaches an instantaneous magnitude 24 sufficient to sustain aglow discharge in the gas so oner than the instantaneous AC voltage applied between the third conductor and the conductors on the first coversheet reaches an instantaneous magnitude sufficient to sustaina glow discharge in the gas, thereby moving the glow discharge condition from between the first and third conductors to between the first and fourth conductors.

30. A method according to claim 29 further comprising the step of changing the AC voltages applied to the first and second conductors to cause the instantaneous voltagedifference between the second conductor and at least one of the conductors on the second coversheet to reach an instantaneous magnitude sufficient to sustain a glow discharge in the gas sooner than the instantaneous AC voltage applied between the first conductor and the conductors on the second coversheet reaches an instantaneous magnitude sufficient to sustain a glow discharge in the gas, thereby moving the low discharge condition from between the first and ourth conductors to between the second and fourth conductors.

31. A method of moving a plasma discharge in an apparatus wherein first and second conductors that are parallel to each other are also perpendicular to and opposite third and fourth conductors on the outside of a gas-filled, dielectric envelope, wherein a plasma discharge is selectively generated in the gas between the first and third conductors and sustained by AC voltage applied between conductors on opposite sides of the envelope, which AC voltage is not sufficient to initiate a plasma discharge, the method comprising:

causing the AC voltage between the first and third conductors to reach an instantaneous plasmadischarge-sustaining magnitude sooner than the AC voltage between the other conductors reaches such an instantaneous magnitude; and subsequently causing the AC voltage between the second and third conductors to reach an instantaneous plasma-discharge-sustaining magnitude sooner than the AC voltage between the first and third conductors reaches such an instantaneous magnitude, thereby causing the plasma discharge to occur between the second and third conductors rather than between the first and third conductors. 

1. An apparatus wherein a plasma discharge occurs in a gasfilled, dielectric envelope by applying an A.C. voltage between two electrodes on opposite sides of the envelope, characterized by one of the electrodes being tapered with the plasma discharge being applied first near the narrow end of the tapered electrode and progressing in steps toward the wide end on each half-cycle of the applied A.C. voltage which causes a greater capacitive coupling through the dielectric envelope at wider portions of the tapered electrode causing discharge to preferentially occur near the wide end of the electrode.
 2. In a plasma discharge device of the type having a gas sealed in a confined envelope area between a pair of dielectric coversheets, each coversheet having conductors thereon with the conductors being located opposite one another across the gas-filled space, so that ionization of the gas takes place when a predetermined voltage exists across the space between the conductors causing the gas to glow, an improvement including: the dielectric envelope being of a size capable of supporting a plurality of simultaneous glow discharges; means for applying voltage to the conductors; and the shape of the gas filled envelope relative to the shape of at least one of the conductors being such that the area of the gas filled space beneath the conductor varies in a predetermined manner along at least one conductor, so that the application of voltages of different magnitude by the voltage applying means causes discharges to take place in different portions of the envelope corresponding to a predetermined relationship of applied voltage to the gas filled area beneath the electrodes.
 3. An improved apparatus for display or memory, having a first and second dielectric coversheet spaced apart and sealed to form an envelope with a gas therein and at least one conductor on the first coversheet outside of the envelope and at least two conductors on the second coversheet outside of the envelope, means for selectively initiating a glow discharge in the gas between the conductor on the first coversheet and one of the conductors on the second coversheet, and means for continuously applying AC voltage between the conductor on the first coversheet and the conductors on the second coversheet, the AC voltage being of insufficient magnitude to initiate a glow discharge but of sufficient magnitude to sustain a glow discharge, wherein the improvement comprises: means for causing the AC voltage on the one of the conductors on the second coversheet to be reduced relative to the AC voltage on the other of the conductors on the second coversheet, thereby causing the glow discharge condition to migrAte from between the one conductor on the second coversheet and the conductor on the first coversheet to between the other conductor on the second coversheet and the conductor on the first coversheet.
 4. An improved apparatus for display or memory, having first and second dielectric coversheets spaced apart and sealed to form an envelope with a gas therein and at least one conductor on the first coversheet outside of the envelope and at least a first conductor and a second conductor on the second coversheet outside of the envelope, means for selectively initiating a glow discharge in the gas between the conductor on the first coversheet and the first conductor on the second coversheet, and means for continuously applying an AC voltage between the conductor on the first coversheet and the first and second conductors on the second coversheet, the AC voltage being of insufficient magnitude to initiate a glow discharge but of sufficient magnitude to sustain a glow discharge, wherein the improvement comprises: means for changing the AC voltage applied between the first conductor on the second coversheet and the conductor on the first coversheet relative to the AC voltage applied between the second conductor on the second coversheet and the conductor on the first coversheet to cause the instantaneous voltage applied to the second conductor on the second coversheet to reach the magnitude sufficient to maintain a glow discharge sooner than the instantaneous voltage applied to the first conductor on the second coversheet reaches the magnitude sufficient to maintain a glow discharge, thereby causing the glow discharge condition to migrate from between the first conductor on the second coversheet and the conductor on the first coversheet to between the second conductor on the second coversheet and the conductor on the first coversheet.
 5. An apparatus according to claim 4 wherein the changing means comprises means for reducing the AC voltage applied to the first conductor on the second cover-sheet relative to the AC voltage applied to the second conductor on the second coversheet while continuing to maintain the relatively reduced AC voltage at a magnitude sufficient to sustain a discharge.
 6. An apparatus according to claim 5 wherein the reducing means comprises means for holding constant the AC voltage applied to the first conductor on the second coversheet and means for increasing the AC voltage applied to the second conductor on the second coversheet.
 7. An apparatus according to claim 5 wherein the reducing means comprises means for holding constant the AC voltage applied to the second conductor on the second coversheet and means for decreasing the AC voltage applied to the first conductor on the second coversheet.
 8. An apparatus according to claim 5 wherein the reducing means comprises means for decreasing the AC voltage applied to the first conductor on the second coversheet and means for increasing the AC voltage applied to the second conductor to the second coversheet.
 9. An apparatus according to claim 4 wherein the changing means comprises means for varying the phase of the AC voltages to cause the instantaneous voltage applied to the second conductor on the second coversheet to rise sooner than the instantaneous voltage applied to the first conductor on the second coversheet.
 10. An apparatus according to claim 9 wherein the varying means comprises means for holding steady the AC voltage applied to the first conductor on the second coversheet and means for advancing the AC voltage applied to the second conductor on the second coversheet.
 11. An apparatus according to claim 9 wherein the varying means comprises means for holding steady the AC voltage applied to the second conductor on the second coversheet and means for retarding the AC voltage applied to the first conductor on the second coversheet.
 12. An apparatus according to claim 9 wherein the varying means comprises means for retarding the AC voltage applIed to the first conductor on the second coversheet and means for advancing the AC voltage applied to the second conductor on the second coversheet.
 13. An apparatus according to claim 4 wherein at least the second conductor on the second coversheet is generally tapered, having a narrow end and a wide end.
 14. An apparatus according to claim 13 wherein the conductors on the second coversheet are positioned with the narrow end of the tapered second conductor adjacent but not touching the first conductor.
 15. An apparatus according to claim 14 wherein the second conductor is one of a plurality of electrically-connected, generally tapered electrode segments arranged in a line on the second coversheet; and wherein the first conductor is one of a plurality of electrically-connected, generally tapered electrode segments arranged in a line on the second coversheet.
 16. An apparatus according to claim 15 wherein the wide ends of the tapered electrode segments of the first conductor are positioned adjacent but not touching the narrow ends of the tapered electrode segments of the second conductor and the wide ends of the tapered electrode segments of the second conductor are positioned adjacent but not touching the narrow ends of the tapered electrode segments of the first conductor.
 17. An apparatus according to claim 16 further comprising a third conductor on the second coversheet positioned adjacent the wide end of one of the tapered segments on the second coversheet and means for transferring a glow discharge condition from the one tapered segment to the third conductor; the third conductor being tapered, having a wide end and a narrow end, with the narrow end of the third conductor positioned adjacent to but not touching the one tapered segment; and the third conductor being one of a plurality of electrically connected, generally tapered electrode segments arranged in a line perpendicular to the lines of the first and second conductors.
 18. An apparatus according to claim 17 further comprising a plurality of fourth tapered, electrically-connected conductors on the second coversheet arranged in a line parallel with the line of the third conductor; and the fourth conductors being electrically connected to one of the other conductors on the second coversheet.
 19. A shift register for moving data bits generally in a line comprising: a dielectric, gas-filled envelope having two sides; a first pair of conductors on the outside of one side of the envelope, extending parallel to each other and generally along the line; a plurality of orthogonal conductors on the outside of the envelope and on the other side of the envelope and extending generally perpendicular to the first pair of conductors; a plurality of ignition electrodes selectively arranged in a row on the outside of the envelope parallel with the line; means for applying an AC voltage to the ignition electrodes, the magnitude of the AC voltage being sufficient to initiate a plasma discharge at each ignition electrode and within the envelope; means for applying AC voltage between at least one of the first pair of conductors and at least one of the orthogonal conductors, the magnitude of AC voltage being sufficient to sustain a plasma discharge but insufficient to initiate a plasma discharge; and means for controlling the AC voltage applied to the conductors for causing the plasma discharge to progress between the first pair of conductors and the orthogonal conductors generally along the line.
 20. A shift register according to claim 19 further comprising a second shift register arranged generally in a second line intersecting the line of the first shift register and arranged so that a bit-representing plasma discharge progressing along the line on the first shift register is transferred to the second shift register and progresses along the second line on the second shift register.
 21. A shift register according to claim 19 further comprisiNg: a second pair of conductors on the outside of the envelope cooperating with the orthogonal conductors and extending parallel with the first pair of conductors with each conductor of the second pair of conductors associated with a corresponding one of the first pair of conductors; and means for receiving a plasma discharge from the first pair of conductors and in response thereto for initiating progression of the plasma discharge on the second pair of conductors generally along a second line parallel with the line of the first pair of conductors comprising a shift register folded on itself.
 22. A display device comprising: a dielectric, gas-filled envelope; a plurality of shift registers comprising conductors on the outside of the envelope for moving data-bit-representing plasma discharges generally along substantially parallel lines; means associated with each shift register for selectively initiating plasma discharges in the shift registers; a manifold shift register arranged along a line intersecting the parallel lines for receiving plasma discharges from the shift registers and for moving the plasma discharges generally along the intersecting line; and means for receiving plasma discharges from the manifold shift register and for visually displaying the plasma discharges.
 23. A method of controlling a memory condition at a first location between a first pair of electrical conductors and at a second location between a second pair of electrical conductors, a first conductor of the second pair of conductors being tapered with the narrow end of the tapered first conductor being positioned adjacent but not touching a first conductor of the first pair of conductors, no more than a single conductor of the first pair of conductors being in common with no more than a single conductor of the second pair of conductors, comprising the steps of: applying an AC voltage between the first pair of electrical conductors of a magnitude sufficient to maintain the memory condition at the first location; applying an AC voltage between the second pair of electrical conductors; causing the instantaneous voltage applied to the second pair of electrical conductors to reach the magnitude sufficient to maintain a memory condition sooner than the instantaneous voltage applied to the first pair of electrical conductors reaches the magnitude sufficient to maintain a memory condition, thereby causing the memory condition to move to the second location from the first location; and continuing the application of AC voltage between the second pair of electrical conductors, thereby causing the memory condition to migrate to the wide end of the tapered first conductor.
 24. A method of controlling a memory condition at a first location between a first pair of electrical conductors and at a second location between a second pair of electrical conductors, no more than one conductor of the first pair of conductors being in common with no more than one conductor of the second pair of conductors, comprising the steps of: applying an AC voltage between the first pair of electrical conductors of a magnitude sufficient to maintain the memory condition at the first location; applying an AC voltage between the second pair of electrical conductors; and causing the instantaneous voltage applied to the second pair of electrical conductors to reach the magnitude sufficient to maintain a memory condition sooner than the instantaneous voltage applied to the first pair of electrical conductors, thereby causing the memory condition to move to the second location from the first location.
 25. A method according to claim 24 wherein the causing step comprises reducing the magnitude of the AC voltage applied between the first pair of conductors with respect to the AC voltage applied between the second pair of conductors so that the magnitude of the AC voltage between the first pair of conductors is less than the magnitude of the AC voltage between the second pair of conductors but still sufficient to maintain a memory condition.
 26. A method according to claim 25 wherein the reducing is accomplished by holding constant the AC voltage applied between the first pair of conductors and increasing the AC voltage applied between the second pair of conductors.
 27. A method according to claim 25 wherein the causing step further comprises varying the phase of the AC voltages simultaneously with reducing the magnitude of the AC voltage applied between the first pair of conductors with respect to the second pair of conductors to cause the voltage applied between the second pair of conductors to rise sooner than the voltage applied between the first pair of conductors.
 28. A method according to claim 24 wherein the causing step comprises varying the phase of the AC voltages to cause the instantaneous voltage applied between the second pair of conductors to rise sooner than the instantaneous voltage applied between the first pair of conductors.
 29. An improved method of controlling a display or memory device having first and second dielectric coversheets spaced apart and sealed to form an envelope with a gas therein, a first conductor and a second conductor arranged parallel to each other on the first coversheet outside of the envelope, a third conductor and a fourth conductor arranged parallel to each other on the second coversheet outside of the envelope, the third and fourth conductors arranged perpendicular to and overlapping the first and second conductors, means for selectively initiating a glow discharge in the gas between the first conductor and the third conductor, means for continuously applying an AC signal to the first and second conductors, and means for applying an AC voltage to the third and fourth conductors, the AC voltage applied to the conductors on the second coversheet being substantially 180* out of phase with the AC voltage applied to the conductors on the first coversheet so as to produce AC voltage difference between the conductors on the first coversheet and the conductors on the second coversheet which AC voltage difference has a maximum magnitude equal to the sum of the peak-to-peak voltages of the AC voltages applied to the conductors on the two coversheets, the maximum magnitude of the AC voltage difference between the conductors on the first coversheet and the conductors on the second coversheet being of insufficient magnitude to initiate a glow discharge in the gas but of sufficient magnitude to sustain a glow discharge in the gas, wherein the improved method comprises: controlling the AC voltages applied to the first and second conductors so that the instantaneous voltage difference between the first conductor and at least one of the conductors on the second coversheet reaches an instantaneous magnitude sufficient to sustain glow discharge in the gas sooner than the instantaneous AC voltage applied between the second conductor and the conductors on the second coversheet reaches an instantaneous magnitude sufficient to sustain a glow discharge in the gas; controlling the AC voltages applied to the third and fourth conductors so that the instantaneous voltage difference between the third conductor and at least one of the conductors on the first coversheet reaches an instantaneous magnitude sufficient to sustain a glow discharge in the gas sooner than the instantaneous AC voltage applied between the fourth conductor and the conductors on the first coversheet reaches an instantaneous magnitude sufficient to sustain a glow discharge in the gas; and changing the AC voltages applied to the third and fourth conductors to cause the instantaneous voltage difference between the fourth conductor and at least one of the conductors on the first coversheet to reach an instantaneous magnitude sufficient to sustain a glow discharge in the gas sooner than the instantaneous AC voltage applied between the third conductor and the condUctors on the first coversheet reaches an instantaneous magnitude sufficient to sustain a glow discharge in the gas, thereby moving the glow discharge condition from between the first and third conductors to between the first and fourth conductors.
 30. A method according to claim 29 further comprising the step of changing the AC voltages applied to the first and second conductors to cause the instantaneous voltage difference between the second conductor and at least one of the conductors on the second coversheet to reach an instantaneous magnitude sufficient to sustain a glow discharge in the gas sooner than the instantaneous AC voltage applied between the first conductor and the conductors on the second coversheet reaches an instantaneous magnitude sufficient to sustain a glow discharge in the gas, thereby moving the glow discharge condition from between the first and fourth conductors to between the second and fourth conductors.
 31. A method of moving a plasma discharge in an apparatus wherein first and second conductors that are parallel to each other are also perpendicular to and opposite third and fourth conductors on the outside of a gas-filled, dielectric envelope, wherein a plasma discharge is selectively generated in the gas between the first and third conductors and sustained by AC voltage applied between conductors on opposite sides of the envelope, which AC voltage is not sufficient to initiate a plasma discharge, the method comprising: causing the AC voltage between the first and third conductors to reach an instantaneous plasma-discharge-sustaining magnitude sooner than the AC voltage between the other conductors reaches such an instantaneous magnitude; and subsequently causing the AC voltage between the second and third conductors to reach an instantaneous plasma-discharge-sustaining magnitude sooner than the AC voltage between the first and third conductors reaches such an instantaneous magnitude, thereby causing the plasma discharge to occur between the second and third conductors rather than between the first and third conductors. 